1. Field of the Invention
The present invention relates to a MR (magnetoresistive)/inductive combined thin film magnetic head loaded on, for example, a hard disk device, and particularly to a thin film magnetic head comprising a shield layer having a magnetic domain structure stabilized for obtaining stable reproduced signal waveforms in an MR element.
2. Description of the Related Art
FIG. 3 is an enlarged sectional view showing a conventional thin film magnetic head as viewed from the ABS (air bearing surface) side opposite to a recording medium.
This thin film magnetic head is a so-called MR/inductive combined thin film magnetic head comprising a reading head h1 using a magnetoresistive effect and a writing inductive head h2, both of which are laminated at the trailing-side end of a slider, which constitutes, for example, a floating type head.
In the reading head h1, a lower gap layer 2 made of a nonmagnetic material such as Al.sub.2 O.sub.3 (alumina) or the like is formed on a lower shield layer 1 made of sendust or a NiFe alloy (permalloy), and a magnetoresistive element layer 3 is formed on the lower gap layer 2. The magnetoresistive element layer 3 comprises a spin valve film {a GMR (Giant Magnetoresistive) element} having, for example, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer. In the spin valve film, magnetization of the pinned magnetic layer is fixed in the direction perpendicular to the drawing (the depth direction), and magnetization of the free magnetic layer is arranged in the direction of the track width. When a magnetic field enters from a recording medium in the direction perpendicular to the drawing, magnetization of the free magnetic layer is changed to change electric resistance by the relation between fixed magnetization of the pinned magnetic layer and variable magnetization of the free magnetic layer, reproducing a record magnetic field.
Hard magnetic bias layers 4 are formed as longitudinal bias layers on both sides of the magnetoresistive element layer 3. On the hard magnetic bias layers 4 are respectively formed electrode layers 5 made of a nonmagnetic electrically conductive material having low electric resistance, such as Cu (copper), W (tungsten), or the like. An upper gap layer 6 made of a nonmagnetic material such as alumina is further formed on the electrode layers 5.
An upper shield layer 7 is formed on the upper gap layer 6 by plating permalloy or the like so that gap length G11 is determined by the distance between the lower shield layer 1 and the upper shield layer 7. In the inductive head h2, the upper shield layer 7 functions as a leading-side core (lower core layer) for applying a record magnetic field to the recording medium.
A gap layer (nonmagnetic material layer) 9 made of alumina or the like, and an insulation layer (not shown) made of polyimide or a resist material are laminated on the lower core layer 7, and a coil layer 10 formed in a helical pattern is provided on the insulation layer. The coil layer 10 is made of a nonmagnetic electrically conductive material having low electric resistance, such as Cu (copper) or the like. The coil layer 10 is also surrounded by the insulation layer (not shown) made of polyimide or a resist material, and an upper core layer 11 is formed on the insulation layer by using a magnetic material such as permalloy or the like. The upper core layer 11 functions as the trailing-side core of the inductive head h2 for supplying a recording magnetic field to the recording medium.
As shown in FIG. 3, the upper core layer 11 is opposite to the lower core layer 7 with the gap layer 9 held therebetween on the side opposite to the recording medium to form a magnetic gap with a magnetic gap length G12 for supplying a recording magnetic field to the recording medium. Further, a protective layer 12 made of alumina or the like is provided on the upper core layer 11.
In the inductive head h2, a recording current is supplied to the coil layer 10 to supply a recording magnetic field to the upper core layer 11 and the lower core layer 7 from the coil layer 10. As a result, a magnetic signal is recorded on the recording medium such as a hard disk or the like by a leakage magnetic field from the magnetic gap between the lower core layer 7 and the upper core layer 11.
In order to improve stability of signals output from the magnetoresistive layer 3, it is necessary to decrease an inflow of external noise into the magnetoresistive element layer 3. Therefore, it is thought to be necessary that a magnetic field is applied in the direction of the track width during the deposition of the shield layers 1 and 7 or in treatment after the deposition to arrange the uniaxial anisotropic direction of the lower shield layer 1 and the upper shield layer 7 in the direction of the track width so that the direction of the track width becomes the easy axis of magnetization, and the direction (the direction perpendicular to the drawing) perpendicular to the magnetic medium becomes the hard axis of magnetization, thereby preventing magnetization of the shield layers 1 and 7 from adversely affecting the magnetoresistive element layer 3.
However, when each of the lower shield layer 1 and the upper shield layer 7 comprises a single layer made of an NiFe alloy (permalloy), as shown in FIG. 3, the application of a magnetic field in the direction of the track width brings the domain structure of the shield layers 1 and 7 into a multiple magnetic domain state, creating a state wherein magnetic anisotropy is dispersed, as shown in FIG. 4.
Particularly, in the vicinity of the ends of the shield layers 1 and 7, the direction of magnetization is shifted from the direction of the track width, as shown in magnetic domains 13, or perpendicular to the direction of the track width, as shown in magnetic domains 14. As a result of examination of the anisotropic direction in a wafer in the head manufacturing process, in the shield layers 1 and 7 shown in FIG. 4, the variation of the magnetization direction (variation in skew angle) is as large as about .+-.10.degree..
The variation in skew angle represents the angle of deviation of magnetization from the direction of the track width. As the variation in skew angle increases, the magnetic reversibility of the shield layers 1 and 7 deteriorates to deteriorate the shield function, and the magnetoresistive element layer 3 held between the shield layers 1 and 7 is affected by the variation of magnetization of the shield layers 1 and 7. For example, when the magnetoresistive element layer 3 comprises a spin valve film, the magnetic domain of the free magnetic layer in the spin valve film, in which magnetization to be arranged in the direction of the track width, is made unstable, thereby causing Barkhausen noise. Particularly, the effect on the magnetoresistive element layer 3 significantly occurs as the gap length G11 shown in FIG. 3 decreases due to an increase in recording density.
A method of decreasing the variation of skew angle is to improve the magnetic material which constitutes the shield layers 1 and 7. As described above, the shield layers 1 and 7 shown in FIG. 7 are made of an NiFe alloy which exhibits an anisotropic magnetic field Hk of as low as about 2 to 4 (Oe), and thus the magnetic domain structure of the shield layers 1 and 7 made of the NiFe alloy is readily made unstable, thereby increasing the variation in skew angle. Therefore, by using a material having a higher anisotropic magnetic field Hk than the NiFe alloy, for example, a CoZrNb alloy (Hk=about 7 to 12 Oe), for the shield layers 1 and 7, the variation in skew angle of the shield layers 1 and 7 can be decreased.
FIG. 5 is a plan view showing the magnetic domain structure of shield layers 1 and 7 made of a magnetic material having a high anisotropic magnetic field Hk, such as a CoZrNb alloy or the like.
It was confirmed that the formation of the shield layers 1 and 7 using a magnetic material having a high anisotropic magnetic field Hk, such as a CoZrNb alloy or the like, permits a decrease in the variation of skew angle to about .+-.1.degree..
However, the magnetic domain structure is further subdivided, as shown in FIG. 4. Although the magnetic domains 13 and 14 shown in FIG. 4, in which the direction of magnetization is shifted from the direction of the track width shown in FIG. 3, are made small, such domains actually occur near the ends of the shield layers 1 and 7 shown in FIG. 4.
In this way, by using a magnetic material having a high anisotropic magnetic field Hk for the shield layers 1 and 7, the variation in the skew angle can be decreased, and the effect on improvement in the shield function and the magnetoresistive element layer 3 can be decreased, as compared with the shield layers 1 and 7 made of an NiFe alloy. However, the most preferable magnetic domain structure for the shield layers 1 and 7 is a structure in which magnetization is put into a single magnetic domain state in the direction of the track width. This structure cannot be realized by the conventional shield layers 1 and 7.
The lower shield layer 1 formed below the magnetoresistive element layer 3 has only the shield function, while the upper shield layer 7 formed above the magnetoresistive element layer 3 has not only the shield function but also the function as the lower core of the inductive head. Therefore, it is necessary to simultaneously improve the shield function and the core function.
However, since properties required for improving the shield function are different from those required for improving the core function, it is difficult to simultaneously improve both the shield function and core function when the upper shield layer (lower core layer) 7 comprises a single layer, as shown in FIG. 3.